Involvement of the dorsal periaqueductal gray in the loss of fear-potentiated startle accompanying high footshock training.

Abstract

The amplitude of acoustic startle is markedly enhanced by cues signaling moderately intense footshocks but, surprisingly, not by cues signaling higher intensity footshocks. Previous findings suggest that the ineffectiveness of high footshock training may involve activation of the dorsal periaqueductal gray (PAG). As a means of evaluating this possibility, rats trained with moderate (0.6 mA) footshocks were later tested after intra-PAG infusion of an excitatory nontoxic dose of kainic acid. Kainic acid significantly reduced fear-potentiated startle relative to vehicle controls. In a 2nd experiment, the effect of dorsal PAG lesions on fear-potentiated startle to cues paired with 0.6-mA and 1.6-mA footshocks was evaluated. Dorsal PAG lesions prevented the disruptive effects of high footshock training. Together, these results suggest that dorsal PAG activation mediates the loss of potentiated startle accompanying high footshock training.

Affective and neuroendocrine effects of withdrawal from chronic, long-acting opiate administration

“…Preliminary analysis of startle data revealed no main effects on potentiated startle, or interactions, as a function of startle stimulus intensity. This is consistent with other measures of potentiated startle (Walker and Davis, 1997), and hence this factor was excluded from further analyses. Presence of diarrhea was compared between groups using Chi-square analysis.…”

Fear-Potentiated Startle in Rats Is Mediated by Neurons in the Deep Layers of the Superior Colliculus/Deep Mesencephalic Nucleus of the Rostral Midbrain through the Glutamate Non-NMDA Receptors

“…However, these lesions were relatively large, and gliosis was present in the area lateral to the PAG. More confined lesions that covered only the dorsal and lateral PAG did not block fear-potentiated startle (Walker and Davis, 1997), and we did not find that infusion of NBQX into the PAG blocked fear-potentiated startle at a dose that appeared to diminish context-induced freezing, although admittedly only partially, consistent with the known role of the PAG in freezing (Blanchard et al, 1981;Zhang et al, 1990;Kim et al, 1993;Bandler and Shipley, 1994;Fanselow, 1994;Morgan et al, 1998). Because the infusion site of NBQX in this study was in the dorsal/lateral PAG, the incomplete blockade of contextual freezing by NBQX may have been attributable to only partial diffusion into the ventrolateral PAG.…”

“…Lesions directed to the PAG (Fendt et al, 1996) or MRF (Frankland and Yeomans, 1995) both included some damage to the deep SC/DpMe that sits between the PAG and the MRF. More confined lesions of the dorsal and lateral PAG (Walker and Davis, 1997), or lesions of the auditory thalamus that partially involved in the MRF (Campeau and Davis, 1995), did not block fear-potentiated startle using a visual conditioned stimulus (CS), indirectly implicating the deep SC/DpMe as the critical site that mediates fear-potentiated startle.…”

Neural Correlates of Fear in the Periaqueductal Gray

“…It is generally thought that the PAG is downstream of the amygdala and prefrontal cortex, generating the appropriate defensive response to fearful or threatening events (Tovote et al, 2016). The networks that coordinate innate behaviors include dorsal regions of the PAG (dorsal PAG, dPAG; including dorsal, dorsolateral, and lateral columns; Bandler and Depaulis, 1988; Fanselow et al, 1991; Walker and Davis, 1997; De Oca et al, 1998; Vianna et al, 2001a), whereas those that orchestrate learned behaviors include the ventral PAG (vPAG; notably its ventrolateral column; Bandler and Shipley, 1994; Bandler et al, 2000; Vianna et al, 2001b; Helmstetter et al, 2008). Depending on context (e.g., proximity of threat), both innate and learned defense behaviors include freezing (Bowen et al, 2013; Koutsikou et al, 2014).…”